The subjects described above are generally known. Purely by way of example, reference is made to JP 04-158 912 A and JP 06-210 338 A.
DE 33 03 829 A1 discloses an operating method for a multi-stand rolling mill train, in which method, inter alia, the peripheral precession of a strip in a roll nip of a rolling stand is determined. The inlet-side and the outlet-side strip thickness, inter alia, are required to determine the peripheral precession.
In the case of multi-stand cold-rolling mills, the strip thickness—i.e. the thickness with which the strip exits in each case one of the rolling stands—is generally only measured downstream from the first and downstream from the last rolling stand. No such measurement of the strip thickness takes place downstream from the remaining rolling stands of the rolling mill train (intermediate stands). Strip thickness defects may therefore arise as a result of the rolling in the intermediate stands, and these defects are only detected downstream from the last rolling stand. Although, in the prior art, a control command is determined for the last or the penultimate rolling stand of the rolling mill train and output to the corresponding rolling stand owing to the detection of the strip thickness defect, this procedure only makes it possible to correct strip thickness defects which occur with a relatively long delay. This is true particularly when the control command is intended for the penultimate rolling stand of the rolling mill train. Furthermore, only late correction of a strip thickness defect which has occurred takes place.
Complete correction of a strip thickness defect is also not always possible.
It would be advantageous if the strip thickness with which the strip exits the respective rolling stand were known for each rolling stand. This is because strip thickness defects which have occurred could then be corrected immediately or other measures could be taken.
For this purpose, it is conceivable to arrange a thickness-measuring device downstream from each rolling stand. However, thickness-measuring devices are expensive and therefore are not used in practice.
Furthermore, it is conceivable to detect the rolling force, with which the strip is rolled in the intermediate stand, for each intermediate stand, and to determine, on the basis of the set roll nip of said intermediate stand and the respective rolling force in conjunction with the spring constant of the respective intermediate stand, the extent to which the intermediate stand in question expands, and to thus determine the effective roll nip and therefore the strip thickness. However, this procedure is too inaccurate and is therefore not employed in practice.